This application claims priority to an application entitled xe2x80x9cChannel Assigning Device and Method in CDMA Communication Systemxe2x80x9d filed in the Korean Industrial Property Office on Dec. 7, 1998 and assigned Serial No. 98-54052, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates generally to a communication device and method in a CDMA (Code Division Multiple Access) communication system, and in particular, to a device and method for assigning a channel while in a conversation state.
2. Description of the Related Art
The next-generation CDMA mobile communication system will use more channels than the present CDMA communication system. The CDMA link is comprised of common channels and dedicated channels. The dedicated channels include a fundamental channel (FCH) for processing a voice signal, a supplemental channel for transmission of packet data, and a dedicated control channel (DCCH) for transmission of control information.
In the next-generation CDMA mobile communication system, some mobile stations (MSs) can request fundamental channels and other MSs can request dedicated control channels. There will exist MSs which can request both the fundamental channels and the dedicated control channels concurrently, depending on their BSPs (Bearer Service Profiles). Here, the fundamental channel can transmit voice and the dedicated control channel can transmit packet data.
However, the dedicated control channel cannot be requested, let alone both the dedicated channel and the fundamental channel concurrently, in the IS-95 CDMA scheme. If an MS sequentially requests a fundamental channel and a dedicated control channel, the first requested channel can be assigned on a paging channel but the next requested channel cannot be assigned on the paging channel. That is, while a communication is in progress using a dedicated channel, a fundamental channel or a dedicated control channel should be assigned on the dedicated channel in the communication state. Therefore, a method is needed in which a fundamental channel or dedicated control channel assignment message is transmitted/received on a channel other than a paging channel, for channel assignment.
To add new dedicated channels (fundamental channels or dedicated control channels in the communication state), there is a need for an encoding method which can increase channel capacity. One way to increase system capacity in the CDMA communication system is through channelization, which is provided by use of orthogonal codes. The orthogonal codes can be Walsh codes, as are the orthogonal channels in the forward link of the IS-95 standard, for example.
Orthogonal channelization is provided in an IS-95 communication system to the forward link by establishing a transmission channel and notifying the channel receiving device of the established channel by a channel transmitting device. The following description is conducted on the assumption that the transmitting device is a base station (BS) and the receiving device is an MS. Each transmission and reception channel on the forward link is distinguished by its assigned orthogonal code. It is also assumed that each channel on the IS-95 forward link is convolutionally encoded and a modulator performs BPSK (Bi-Phase Shift Keying) modulation. The bandwidth used is 1.2288 MHz and the data rate is 9.6 kbps, in the IS-95 system. Therefore, 64 channels (=1.2288M/(9.6 kxc3x972)) on an IS-95/IS-95A forward link are distinguished by 64 orthogonal codes.
To operate the CDMA system having the above channel structure, channel assignment and channel release should be implemented accurately and stably, and a mobile capability should be considered for requesting and assigning a fundamental channel and a dedicated control channel between a BS and an MS. However, the above scheme limits the number of available channels, due to the limited number of orthogonal codes available. Quasi-orthogonal codes, which provide minimized interference with the orthogonal codes, can be used to overcome the above problem. The length of an orthogonal code varies with the data rate in mobile communication systems which use a variable data rate. Therefore, it is preferable to use quasi-orthogonal codes due to its advantage of minimum interference with orthogonal codes.
However, a transmitting/receiving device in an IS-95 communication system is configured without considering the possibility of using quasi-orthogonal codes for assigning a forward link channel. Thus, a different channel assignment scheme or transmitting/receiving device is needed for application of the quasi-orthogonal codes.
It is, therefore, a first object of the present invention to provide a channel assigning device and method for a BS in a CDMA communication system, in which the BS uses a dedicated channel currently in use in order to send setup information about assigning another dedicated channel.
It is a second object of the present invention to provide a channel assigning device and method for a BS in a CDMA communication system, in which the BS uses a dedicated channel in current use in order to send setup information about assigning another dedicated channel to an MS, when the MS requests assignment of another dedicated channel while in a conversation state.
It is a third object of the present invention to provide a channel assigning device and method for an MS in a CDMA communication system, in which upon receipt of a channel assignment message on a channel in current use, the MS assigns a corresponding channel indicated by the channel assignment message from the base station.
It is a fourth object of the present invention to provide a channel assigning device and method for an MS in a CDMA communication system, in which the MS requests assignment of another channel in a conversation state, and assigns the channel upon receipt of a channel assignment message on a channel in current use.
It is a fifth object of the present invention to provide a channel assigning device and method for a BS in a CDMA communication system, in which the BS can selectively assign an orthogonal code or a quasi-orthogonal code for a dedicated channel depending on the amount of channel use.
It is a sixth object of the present invention to provide a channel assigning device and method for an MS in a CDMA communication system, in which the MS can selectively assign an orthogonal code or a quasi-orthogonal code for a dedicated channel depending on the amount of channel use.
To achieve the above objects, there is provided a channel assigning device and method in a CDMA communication system. According to an embodiment of the present invention, in a channel assigning method for a base station, the base station establishes a first dedicated channel and communicates with a mobile station on the established first dedicated channel. Then, the base station determines the type of a second dedicated channel and channel spreading code information upon request for additional assignment of the second dedicated channel while in the conversation state, assigns the second dedicated channel, and generates a channel assignment message including the determined channel assignment mode and channel spreading code information to assign the second dedicated control channel. The base station transmits the channel assignment message to the mobile station on the first dedicated channel.